Premiere Pro CS4 imports my AVI file's audio, but video playback does not match up; that is, the audio will playback until finish, but it appears that the video portion only reaches the third or fourth frame of the video! All other video formats import just fine.

Basically you are trying to use non-video material, at least material not really suitable for editing, so you have to find external codecs to handle that or use a more consumer oriented package like Elements.

Others have reported your results - they could edit mjpeg in CS3 and not CS4. I added an mjpeg codec on my CS3, and I know that CS3 did not include an mjpeg codec. So I believe that you, and others, had an mjpeg added that CS3 could use (e.g. by a program that came with the camera or some other system). So far, no one has reported that CS4 works on mjpeg unless they have added an mjpeg codec. But perhaps we haven't heard.

Thanks to everyone for your responses. I solved the problem by installing the proper codec (LEAD MJPEG).

Now I have another problem -- when scrubbing through videos, it seems as if the audio doesn't follow the cursor. That is, if I scroll to the MIDDLE of a video, I hear audio from the BEGINNING of the video, as if I had just paused and resumed.

What could be the problem here?? This appears to happen for DivX movies, which I actually don't use often. But still, this would be a nice problem to solve.